The present invention relates to data storage, and more particularly, to a tape header format which provides efficient and robust codeword interleave designation (CWID) protection for use in a tape storage system.
In modern magnetic tape storage devices, data which is written on the tape is protected by one or more error correction code (ECC). For data correction, data which is read from the tape is conceptually arranged into a large matrix and is protected by two orthogonal error correcting codes, referred to typically as C1 and C2. The large data matrix is referred to as a sub data set (SDS). The C1 code is used to correct the rows of the SDS and the C2 code is used to correct the columns. This error correction methodology is very powerful. However, in order for this error correction methodology to work, the data has to be placed into the correct locations in the SDS. If the data's location cannot be determined, then the error correction methodology cannot be applied to this data. Therefore, the data location information is stored in a field called the header.
Hard-decision iterative C1/C2 decoding using error-only decoding significantly improves error rate performance over other conventional decoding methods. To obtain the best possible error-rate performance with hard-decision iterative C1/C2 decoding, it is important to place uncorrectable C1 errors (uncorrectables) at the correct locations in the data set stored to the buffer memory. Codeword interleave designations (CWIDs) stipulate the addresses of a number of byte-interleaved codeword interleaves (CWIs) within a data set. In one such approach, four byte-interleaved codeword interleaves (CWI-4s) are used. Successful decoding of CWIDs is required for correct placement of C1 uncorrectables in the data set. Therefore, strong error protection of the CWIDs is beneficial to ensuring proper placement of the C1 uncorrectables. However, most conventional methods of improving the CWID protection also reduce format efficiency by adding error correction overhead to the existing header format. Furthermore, conventional methods of providing CWID protection may also utilize bits in the tape headers that are reserved (such as for future use, expansion, etc.). This is undesirable.